1. Field of the Invention
The present invention pertains to the field of fiber optics. The invention more particularly concerns a device which provides for the termination of multiple optical fibers in a single ferrule.
2. Discussion of the Background
During the late 1990s and into the early 2000s, optical fiber based data transmission systems flourished. Optical fiber based systems were installed in buildings, between buildings in the same city, between buildings in different cities, and between buildings on different continents.
Optical fibers are also installed on spans which are not so expansive. Optical fibers run between devices, such as host devices used for communication or data transmission, housed within the same building. Multiple host devices are typically installed in rack-like structures. The back side of the rack structure can become entangled with multiple optical fibers. The optical fibers run between host devices located in the same rack and between host devices located on different racks. Finding a single optical fiber out of the large group of entangled optical fibers is a frustrating and time consuming process. Additionally, when optical fibers become entangled some of the optical fibers can be stressed and bent past their permissible bend radii, thus leading to optical power loss of the transmitted signal and potentially a catastrophic fracture failure of the optical fiber itself.
To combat the problem, some end-users have tried to organize the optical fibers by color coding optical fibers and also by grouping some of the optical fibers, in certain locations, together with tie-wraps. A more logical and organized approach to the management of optical fibers is provided by Advanced Interconnection Technologies, a Stratos Lightwave, Inc., company, and is commonly known as flex circuitry which can be an optical backplane. In a basic form, flex circuitry includes a flexible polymer layer onto which is applied optical fibers in a pre-set arrangement and then a second flexible polymer layer is placed on top of the optical fibers and affixed to the first flexible polymer layer so as to encase and protect and maintain the arrangement of the optical fibers. The optical fibers are typically terminated with one or a combination of more than one of the now well known fiber optic connectors, such as MT, MP, MPX, SC, MDDI, LC, HBMT, MU, ST, FC, and other connector form factors.
Terminating flex circuitry is time consuming and labor intensive, since, typically, multiple optical fibers are terminated into a single ferrule. Multi-fiber, single ferrule terminations are complex since each optical fiber must be at approximately the same termination location. Assuming a ferrule accommodates eight optical fibers, and seven of the eight optical fibers are correctly terminated to the desired termination location and then the eighth optical fiber is incorrectly terminated to a shorter length, then the remaining seven optical fibers must be reterminated to the new termination location.
Adding to the overall problem is the fact that known multi-fiber ferrules have their own unique problems. Many known multi-fiber ferrules are molded using precision molding techniques, such as transfer molding or injection molding. Each molding technique is discussed in turn. A ferrule formed by precision molding typically provides apertures for the insertion of optical fibers. The optical fibers are bonded to the ferrule with epoxy. The holes need to provide a clearance of between one-half micro-meters and two micro-meters. Due to the nature of the molding process, there is a slight variation in the true position of the holes relative to the target or intended position of the holes. Also, there is a slight variation in the diameter of the optical fibers. The float of the optical fiber is the combination of the amount of over size of the hole, the true position of the hole, and the size of the diameter of the optical fiber. The optical fiber is then offset, due to the float, away from the intended position which causes the optical fiber to be offset relative to a coupling fiber. The offset results in optical power loss. Such a ferrule 91 is shown in FIG. 1.
The ferrule 91 of FIG. 1 is an MT-style multi-fiber optic device. The device includes a body 92 which has alignment holes 93, 94 and apertures which accommodate terminated ends 95 of optical fibers at a mating end 101, and a window 98. The body 92 is formed by flowing a resin into a mold. It is believed that the resin flows into the mold near locations 99, 100. The optical fibers 97 of the multi-fiber optical cable 96 are inserted into the body 92 until their ends are nearly flush with the mating end 101. Then an adhesive such as an epoxy is introduced into the window 98 so as to affix the multi-fiber optical cable stripped of its matrix 97 to the body 92.
The relatively large mass at the dimensionally critical mating end 101 of the body 92 incurs an associated relatively large shrink rate once the flowable resin solidifies inside the mold. The shrinkage causes the optical fiber apertures and alignment holes 93, 94 to move in undesired and in uncontrolled ways relative to each other. Additionally, the presence of the window 98 causes a warping effect, since, during molding, the flowable resin flows around a core pin which forms the window. Such a flow pattern is unstable and causes differential stresses in the solidified part. The stresses cause the body 92 to warp, thus changing the geometry of the mating end 101 from its ideal form or shape.
Overmolding or injection molding includes flowing the resin around optical fibers in a mold, thus eliminating the clearance between the optical fibers and their associated apertures in the description provided above. However, overmolding does not eliminate the dimensional errors introduced by flowing the resin into the mold at a location far from the mating end.
Thus, there is a need for a method or device which terminates multiple optical fibers of a single ferrule which is less time consuming to assemble, is more reliable, and is more dimensionally accurate than known methods and devices.
Therefore, it is an object of the invention to provide a multi-fiber optic device which is easily assembled.
It is another object of the present invention to provide a multi-fiber optic device which is reliable.
It is yet another object of the present invention to provide a multi-fiber optic device which is dimensionally accurate.
It is still yet another object of the present invention to provide a method of making a multi-fiber optic device.
In one form of the invention, the multi-fiber optic device includes two optical fibers and a body. The body is formed around and adhered to the two optical fibers. The body includes two alignment bosses, a mating end, and a tapered end. Each alignment boss includes an alignment aperture.
In another form of the invention, the multi-fiber optic device includes two optical fibers and a body. The body is formed around and adhered to the two optical fibers. The body includes two alignment bosses, a tapered portion, a mating end, and a tapered end. Each alignment boss includes an alignment aperture. Both of the optical fibers have respective polished ends and splicing ends. The length of both of the two optical fibers are substantially the same, and both of the two optical fibers are substantially parallel to each other. Furthermore, both of the two alignment apertures are substantially parallel to each other and are also substantially parallel to the two optical fibers. The two alignment apertures and the two optical fibers form a plane. The body is substantially symmetric about the plane. The two alignment bosses straddle the two optical fibers. The mating end of the body and the tapered end of the body straddle the two alignment bosses. The mating end of the body and the tapered end of the body straddle the tapered portion of the body. The length of the two optical fibers is greater than the length separating the mating end of the body from the tapered end of the body. The polished ends of the two optical fibers are substantially flush with the mating end of the body.
In yet another form of the invention, the multi-fiber optic device includes two optical fibers, a body, and a sheath. The body is formed around and adhered to the two optical fibers. The body includes two alignment bosses, a mating end, and a tapered end. Each alignment boss includes an alignment aperture. The sheath includes an aperture for receiving the body, and another aperture which is in communication with the other aperture. The second aperture is capable of receiving an adhesive material so that the sheath is bonded to the body.
In still yet another form of the invention, the multi-fiber optic device is made according to a method. The steps of the method are as follows: stripping a matrix away from a multi-fiber optic cable so as to expose optical fibers; inserting the optical fibers into a mold; introducing a flowable polymer into the mold; extracting heat from the mold so that the flowable polymer solidifies around and adheres to the optical fibers so as to form a body having optical fibers; removing the body having optical fibers from the mold; cleaving the optical fibers extending past a first end of the body; cleaving the optical fibers extending past a second end of the body so as to form splicing ends of the optical fibers; polishing the optical fibers adjacent to the first end of the body; inserting optical fibers of a flex circuit through a first aperture of a sheath; positioning the splicing ends of the optical fibers of the body adjacent to ends of the optical fibers of the flex circuit; splicing the splicing ends of the optical fibers of the body to the ends of the optical fibers of the flex circuit so as to form a spliced area; positioning the sheath around the body so as to encompass the spliced area; introducing an adhesive material into a second aperture of the sheath so that the adhesive material contacts the sheath and the body; and curing the adhesive material so that the sheath is bonded to the body.
Thus, the multi-fiber optic device and method of the invention is superior to existing solutions since the resulting device is reliable, is easy to assemble, and has dimensional stability as compared to prior art devices.